Some motors used in an electric compressor etc., of an air conditioning apparatus contain a harmonic component, which is five or seven times the fundamental frequency component, in an induced voltage. In conventional control, an inverter circuit supplying power to a motor is controlled so that the waveform of a phase current flowing to the motor is a sine wave. However, in this control, the motor current may be distorted under the influence of distortion in a motor voltage to cause a torque ripple.
To address this problem, a technique is suggested, which reduces a torque ripple of a motor by preparing a compensation voltage component for cancelling the torque ripple in advance in a table, and adding the compensation voltage to a voltage reference. (See, for example, PATENT DOCUMENT 2.)
On the other hand, in an inverter such as what is called a “capacitorless inverter” (see, e.g., PATENT DOCUMENT 1), which does not include any energy storage element inside, the energy input to the inverter contains a harmonic component when a torque ripple occurs. Then, power-supply harmonic regulations are not satisfied (herein, a power-supply harmonic is a harmonic contained in an input current). To address the problem, a technique is suggested, which reduces current distortion or the torque ripple by controlling the harmonic component of a motor current extra. (See, for example, PATENT DOCUMENT 3.)